Reference Guide User Manual

8. Appendix—Modbus Additional Information .........................................................................55
8.1 Modbus Tutorial ...................................................................................................55
8.2 Modbus Modes ....................................................................................................55
8.3 Protocol Overview ................................................................................................56
8.4 General Message Formats ...................................................................................56
8.5 RTU Message Format ..........................................................................................56
8.5.1 Computer (Master) Message Format ................................................................56
8.5.2 Device (Slave) Response Format .....................................................................57
8.6 ASCII Message Format ........................................................................................57
8.6.1 Computer (Master) Message Format ................................................................57
8.6.2 Device (Slave) Response Format .....................................................................57
8.7 IP Message Format..............................................................................................58
8.7.1 Computer (Master) Message Format ................................................................58
8.7.2 Device (Slave) Message Format ......................................................................58
8.8 Data Addresses (Registers) .................................................................................58
8.9 Function Codes ....................................................................................................59
8.10 Standard Message Formats .................................................................................59
8.10.1 Read Holding Registers ................................................................................60
8.10.2 Write Holding Register ..................................................................................60
8.10.3 Write Holding Registers ................................................................................60
8.10.4 Mask Write Register......................................................................................61
8.10.5 Report Slave ID ............................................................................................62
8.11 Instrument Manufacturer Data Types ...................................................................63
8.11.1 Short .............................................................................................................63
8.11.2 Unsigned Short .............................................................................................63
8.11.3 Long .............................................................................................................63
8.11.4 Unsigned Long..............................................................................................64
8.11.5 Float .............................................................................................................64
8.11.6 Double ..........................................................................................................64
8.11.7 Character ......................................................................................................64
8.11.8 String ............................................................................................................64
8.11.9 Time .............................................................................................................65
8.12 Exception Codes ..................................................................................................66
8.13 Extended Exception Codes ..................................................................................67
8.14 Probe Register Map Layout .................................................................................68
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